Liquid repellent, vapor permeable microporous materials that repel water, oil, and other low surface tension fluids have utility for example, as fabrics for waterproof garments and tents, as breathable liners for gloves and clothes, as breathable backings for diapers and disposable products, and as protective covers for biological indicators. The value of these materials lies in their ability to repel a wide range of fluids while permitting the rapid transfer of water vapor through the material.
Commercially available fabrics which have been treated with hydrophobic liquids or polymeric materials such as silicone or fluorocarbon oils or resins to render the fabrics fluid repellent but moisture vapor permeable are well known. While these materials can provide adequate repellency properties along with good moisture vapor transmission properties, their durability is variable as some of the barrier treatments, particularly on microporous substrates, are subject to failure if rubbed, touched, abraded or otherwise contacted or flexed. Additionally, these materials typically do not show long term retention of their repellency properties in garment applications where they are exposed to perspiration, presumably because the barrier treatments are readily contaminated by perspiration residues.
U.S. Pat. No. 4,194,041 (Gore et al.) is representative of a number of patents which describe coatings or laminates purported to provide waterproof articles which do not leak when touched and are breathable. This patent describes a layered article for use in waterproof garments or tents comprising at least two layers: an interior, continuous hydrophilic layer that readily allows water vapor to diffuse therethrough, prevents the transport of surface active agents and contaminating substances such as those found in perspiration, and is substantially resistant to pressure induced flow of liquid water, and a hydrophobic layer that permits the transmission of water vapor and provides thermal insulating properties even when exposed to rain. The hydrophobic layer is preferably waterproof microporous tetrafluoroethylene (PTFE) or polypropylene, which permits the passage of moisture vapor through the pores thereof. The hydrophilic layer transfers moisture vapor therethrough whereupon it passes through the porous hydrophobic layer. Various means of joining the layers are suggested including the application of hydraulic pressure to force the hydrophilic polymer to penetrate into the surface void spaces of the hydrophobic layer.
U.S. Pat. No. 4,443,511 (Worden et al.) discloses a layered waterproof, breathable and stretchable article for use in, for example, material for protective articles. Also disclosed is a waterproof and breathable elastomeric polytetrafluoroethylene layered article bonded to a stretch fabric. The water proof and breathable elastomeric polytetrafluoroethylene layered article bonded to a stretch fabric is described as durable and possessing a moisture vapor transmission rate exceeding 1000 gms/m.sup.2 day.
U.S. Pat. No. 4,613,544 (Burleigh) describes a waterproof, moisture vapor permeable unitary sheet material comprising a microporous polymeric matrix having pores comprising continuous passages extending through its thickness and opening into the opposite surfaces thereof, the passages being sufficiently filled with a moisture vapor permeable, water impermeable, hydrophilic material to prevent the passage of water and other liquids through the unitary sheet material while readily permitting moisture vapor transmission therethrough rendering the sheet material breathable. The unitary sheet is made by causing a liquid composition comprising the hydrophilic material or precursor thereof to flow into the pores of the matrix, then causing the conversion thereof to solid hydrophilic material.
While these materials alleviate some of the problems known to the art, many require lamination to protect the water repellent, moisture vapor permeable material they use in their constructions while others require void filling which can lower the moisture vapor transmission rate of the material and decrease its ability to heat seal. Joining of multiple pieces of these materials in a three dimensional garment presents additional problems in that most of these materials are not readily joined together by any means other than sewing which creates needle holes that must be subsequently sealed with seaming tapes or alternative filling techniques to provide a totally waterproof garment. Also, due to the dense nature of the hydrophilic layer, many of these materials are minimally permeable to air.
U.S. Pat. No. 5,025,052 (Crater et al.) describes fluorochemical oxazolidinone compositions and their use for oil and water repellency in films, fibers, and nonwoven webs.
U.S. Pat. No. 4,539,256 (Shipman) discloses a microporous sheet material formed by liquid-solid phase separation of a crystallizable thermoplastic polymer with a compound which is miscible with the thermoplastic polymer at the melting temperature of the polymer but phase separates on cooling at or below the crystallization temperature of the polymer.
U.S. Pat. No. 4,726,989 (Mrozinski) discloses a microporous material similar to that of Shipman but which also incorporates a nucleating agent.
U.S. Pat. No. 4,867,881 (Kinzer) discloses an oriented microporous film formed by liquid-liquid phase separation of a crystalline thermoplastic polymer and a compatible liquid.